Piano recording



May 21, 1935.

IIIIIIIIIIIIIIIIIIII/Il PIANO RECORDING Filed July 15, 1932 1 ==-5s I '8 AMPLIFIER INVENTOR. 66 65 John Hap Hammond Jr. f l r ATTORNEYS Patented May 21, 1935 PIANO RECORDING John Hays Hammond, In, Gloucester, Mass.

PATENT oFFlcg Application July 15, 1932, Serial No. 622,606 8 Claims. (01; 179-1004) This invention relates to musical instruments and more particularly to an improved means for recording the music therefrom.

The invention relates particularly to the recording of the music of a piano and means for eliminating the thump in this music which is produced when the hammers hit the strings of the instrument. V

The invention further provides means for picking up the music of the piano either from the sound board or from a microphone located over the strings and for recording this music on a permanent record such ason' a phonographdisk record or on a moving photographic film.

The invention also consists in certain new and original features of construction and. combinations of parts hereinafter set forth and claimed.

Although the novel features which are believed to be characteristic of this invention will be particularly pointed out in the claims appended hereto, the invention itself, as to its'objects and advantages, the mode of its operation and the manner of its organization may be better understood by referring to the following description taken in connection with the accompanying drawing forming a part thereof, in which the single figure represents diagrammatically a system according to the invention.

In the following description and in'the claims, parts will be identified by specific names for convenience, but they are intended to be as generic in their application to similar parts as the art will permit. r

' Referring to the form of the invention shown in theaccompanying figure, a piano H is provided with the usual strings I 2 and sounding board l3. Connected to this sounding board is 'an electro magnetic pickup device M which is connected by two conductors I 5 and"; to one set of poles of a double pole, double throw switch IT. The other set of poles of this switch is connected to the secondary of a transformer l8, the primary of which is connected by three wires I9, 2| and 22 to a microphone 23. In the line 2| is a battery 24. r

To the other side of switch I! is connected a. potentiometer 25, which is connected to the input circuit of a space discharge device 26. A biasing battery 21 is provided in this circuit. The filament of the device 26 is heated by a battery 28. The output circuit of this device in cludes a B-battery 29 and the primary of a transformer 31. One side of the secondary of the transformer 3| is connected through a blocking condenser 32 to the grid of a space discharge amplifier 33. This grid is connected through a resistance 34 to a condenser 35, the other side of which is connected to the secondary of the transformer 3|. Across the condenser 35 is a biasing resistance 36,

Across this resistance 36 is connects Series a rectifier 31,, and the secondary of a tra rmer 38. One side of the primary of the tran mer 38 1s connected'to the plate of a space di a 6 device 39. The grid of this device is conne g 5 by a conductor 4| to one side of the seconda of the transformer 3|.

The filaments of the devices 33 and 39, are supplied with alternating current through a transformer 44 from a supply 45. A resistance 45 is connected across the filaments of devices 33 and 39. The centralpoint of this resistance is ground ed and is also connected to a battery 41', the

' other side of which is connected. to the cathode former 38.

The other side of the primary of the transformer 52 isconnected through an inductance .53 to the plate of the device as. This plate is connected to ground through a condenser 54. Across the primary of the, transformer 52 is a resistance 55 and a condenser 55.

' The secondary of the' transformer 52 is connected to the input of an amplifier 51, the output of which is connected to a double pole, double throw switch 58. One set of poles of this switch are connected to a phonograph engraving mechanism 59, which is provided with an engraving tool 6|, which is usedfor engraving a record 62. This record is carried on a turn table 63 mounted on a shaft 64, which is rotated by standard phonograph mechanism mounted in a casing 65; R0- tatably mounted on this casing is a bracket 66 to which is pivoted an arm 61 which carries the engraving mechanism 59. The bracket 66 is slowly rotated by means of a mechanism in the casing 65 so that the engraving tool 6! is caused to cut a spiral groove in the record 62 in a manner well known in the art.

The other poles of the switch 58 are connected to a variable intensity lamp 63 which is mounted in a casing 69. Mounted in this casing is a lens 1| which focuses the light from the lamp 68 through a slit '12 on to a moving photographic film i3, which is used for recording the piano music.

In the operation of the system shown in the accompanying figure, if it is desired to pick up the music from the piano by the microphone 23, the switch I! is thrown to the left, thereby connecting the microphone to the input circuit of the device 26 through the potentiometer 25. If, however, it is desired to pick up the music of the piano from the soundboard l3, the switch I! w qi p tioci c c a d ain-ratio.

sistance.

is thrown to the right, thereby connecting the M to t input circuit of the dedg vl ilt cu m'r either the microphone 23 or the pickup device I i 1s amphfied by the ampufier The utpit voltage from the transformer 3| thenpasss through the stoppage condensersz to the mJIIfiBI' 3 3 and also to the con- 01 deV-ICB T18 ampllfied current from the control device ggpasses through the transformer 0 38 and is rectifid by the rectifier 3?.

This rectifier current flows through the re- Sistance -the direction-of-the arrow causing a potential .lfference to be bu lt up across this resistance /hich is proportional to thecurrent 5 flowing ough it and therefore to the nput s gh gth. In this way, as the signal inji all increasing positive potential will be 'p on thevgridof ,the device thereby de- 1 ng its impedance and therefore increasing clef I i As ,the r ,acity 35 is ,large this,action'will be compara- ;vely slow, so that during .abrief interval, after the note is struck the an plifica'qi0. factor will be s a ime il ven @n a eudd nsur c th a pl fi d ene T e amp ifica on tee e ho wi s iadu -l yincree'ee, so thata ter t nit a peak du o t blow on he st is v the amplification factor will increase to .a maxin tm and h radually dec ease as the in u ene y crease h amp f d ent f m t d v c then p s es thr u h th nsformer i to th amp e 5.1 Where it i amp ified and fed e e to the phonograph engraving mechanism 53 for recording on the record- 62 or to the variable i ht ource 8 fo r co ding n the fi 3. pending on whether the switch 38 is thrown .dOWn

or u

' Tlge circuit consisting .of the condenser 35 and the resistance 36 forms a delavaction system, the 'Iill'lfi of action of which may be varied as .desired b u ab y prene t on h capa t and The time of delay determines how much of he ini ia ener y f each n te is Wit held and thus the amount of thump that is .elimllet s Tl con e ers 1 and and e inductance 3 fa m a filter Wo k wh ch cuts u a y undesirable h gh f en y o es wh c a be pres thus e im atin th scra ch from the record, By using this system itis thus seen that it s ossibl to re o d he play of a piano without producing any undesirable peaks or t u p in t i r pr du tion.

Although only a few of the various forms in which this invention may be embodied have been shown h rei it is t b und o that h inention i n t limit d to any sp cifi c uc i n, but might be embodied in various forms without departing from the spirit of the invention .or the sca e oi he app nd d claims.

What is claimed is:

1. In a sound recording system, a piano, means for picking up the vibrations of said piano, an amplifie for ampli in a d i a means aeeee eted i said m ifi o varying the amplification factor of same in accordance with the input signal strength so that strong signals are amplified more than weak ones, said latter means being arranged so that its action is retarded so that the initial surge of energy caused by the striking ,of a note is amplified less than the rem n ns energ of sa d. note a d m n for eerding sa d v b at n o a und e o d ta -11.; a sy m fo re ordin pi o music, a

piano, pickup devices associated therewith, an amplifier for amplifying the energy picked up by said devices, means associated with said amplifier for decreasing the initial surge of energy when a note is struck and means for recording the amplified energy on a sound record tablet.

3. In a sound recording system, a piano, a mi crophone for picking up the vibrations of the piano through the air, a sound board pickup for picking up the vibrations of the sound board, an amplifier for amplifying the energy from either the microphone or sound board pickup, means in combination with said amplifier for diminishing the energy peak due to the striking of a note and means for recording the output of said amplifier a p en s eanhic record blank.

4,. In a soundrecording'system a pianmmeans for picking up the vibrations .of said piano, a space discharge amplifier for amplifying the energy from said pickup means, a spacedischarge a c,ur,-rent .to how through said resistance which causes a positive potential to be built upon the I grid of said amplifier so that the amplification factor 0f said amplifier is varied in accordance with the input-signal strength, means for retarding the building up of said positive potential so that the amplification factor will remain small during the initial peak of energy when .a note is struck and means for recording the output of said amplifier on a sound record tablet.

5. In .a recording system, a piano, means for picking up the vibrations of said piano, a space discharge amplifier having an anode, a cathode and a control element, means for varying the potential on said control element in accordance with the energy picked up from said piano, means for retarding this action so that it is comparatively ineffective during the initial stages of the surge of energy when a note is struck and means for recording the output of saidampli-fier on a phonographic record blank.

6, In a sound recording system, a musical instrument, a pickup device associated therewith, a blank record, a recording devicetherefor, and means between said "pickup device and said recording device for expanding the volume ratio between loud and soft notes, said means being controlled by the dynamics of the sound itself, and means for delaying expanding action to prevent recording of an initial thump when a note is played.

7. The method of recording sound which comprises picking up and amplifying sound energy, automatically varying the amplification of said energy according to the moving average thereof to increase the gain when the input energy level is high and decrease the gain when said input energy level is low and recording said amplified energy upona sound record.

8. In a sound recording system, a pick-up device for picking up the sound to. be recorded, an amplifier fed by said pick-up device, a control circuit also fed by said pick-up device for controlling the gain of said amplifier so that said gain increases with increase in the average intensity of the sound and decreases with decrease in the average intensity of the sound, a blank record, and a recording device for said record fed by said amplifier.

JOHN HAYS HAMMOND, J R. 

